1. Field of the Invention
This invention relates to a lubricating finish that is especially suited for spandex fibers. More particularly, the invention concerns such a finish comprising polydimethylsiloxane and an ethoxylated aliphatic alcohol, a method for preparing the finish and spandex fibers lubricated with the finish. The finish decreases the tackiness of spandex fiber.
2. Description of the Prior Art
Spandex filaments are very tacky compared to conventional textile filaments, such as those melt-spun from nylon or polyester polymers. Spandex filaments tend to stick to each other, especially when wound on a pirn, bobbin, cake or other such yarn package. Tackiness can manifest itself in fused filament segments and high yarn-to-yarn friction. Also, on being unwound from a yarn package, spandex filaments can experience excessive tension and large, rapid transient increases in tension, which in turn lead to many broken filaments during operations such as covering, knitting, weaving and the like. Further, because spandex filaments are subjected to higher compressive forces when they are located in the inner layers of a wound up yarn package, as compared to the compressive forces on the filaments in the outer layers, average tensions and numbers of tension transients can change significantly as the filaments are unwound from the yarn package. Such tension variations produce nonuniformities in fabrics made with spandex fiber supplied from such packages.
Various finishes have been suggested for lubricating the surfaces and reducing the tackiness of spandex filaments. A finish for spandex filaments, which has been used with considerable success in commercial operations, comprises by weight about 92 parts of polydimethylsiloxane, 4 parts of polyamylsiloxane and 4 parts magnesium stearate. Similar finishes are disclosed by Chandler, U.S. Pat. No. 3,296,063. The finishes can be applied to the spandex filaments by dipping, padding, spraying, finish rolls or by addition to spandex polymer spinning solution for simultaneous extrusion with the fiber-forming spandex polymer. The finishes usually amount to between about 2 and 8 percent of the weight of the filament to which they are applied.
Buster et al, U.S. Pat. No. 3,634,236, discloses a finish for use on spandex fibers. The finish comprises a solution of mineral oil and silicone oil (e.g., formed in part by polydimethylsiloxane, among others) and surfactant (e.g., an ethoxylated alkyl alcohol of 8 to 20 carbon atoms). However, mineral oil finishes often cause swelling of spandex fibers and are generally inferior to the commonly used commercial finish described in the the preceding paragraph.
An object of the present invention is to provide a surface finish for spandex fiber which decreases the tackiness of the fiber, provides satisfactory frictional characteristics to the fiber surface and thereby permits more efficient utilization of the fiber in yarn-covering and fabric-making operations.